Calcium Hydroxyapatite: A Highly Stable and Selective Solid Catalyst for Glycerol Polymerization

Negisa Ebadipour,Franck Dumeignil,Sébastien Paul,Benjamin Katryniok

doi:10.3390/catal11101247

Abstract

Calcium-based catalysts are of high interest for glycerol polymerization due to their high catalytic activity and large availability. However, their poor stability under reaction conditions is an issue. In the present study, we investigated the stability and catalytic activity of Ca-hydroxyapatites (HAps) as one of the most abundant Ca-source in nature. A stochiometric, Ca-deficient and Ca-rich HAps were synthesized and tested as catalysts in the glycerol polymerization reaction. Deficient and stochiometric HAps exhibited a remarkable 100% selectivity to triglycerol at 15% of glycerol conversion at 245 °C after 8 h of reaction in the presence of 0.5 mol.% of catalyst. Moreover, under the same reaction conditions, Ca-rich HAp showed a high selectivity (88%) to di- and triglycerol at a glycerol conversion of 27%. Most importantly, these catalysts were unexpectedly stable towards leaching under the reaction conditions based on the ICP-OES results. However, based on the catalytic tests and characterization analysis performed by XRD, XPS, IR, TGA-DSC and ICP-OES, we found that HAps can be deactivated by the presence of the reaction products themselves, i.e., water and polymers.

Highlights

Polyglycerols (PGs) are very interesting polyols with a wide range of structures and applications, in the cosmetics, biomedical, and food sectors
Considering the wide availability of Ca, its low cost, and its absence of toxicity in the case of catalyst leaching into the media, Ca-based catalysts can be especially considered promising for glycerol polymerization reactions [9,12]
The results showed that HAp-S and HAp-D exhibited the same catalytic performances: 15% glycerol conversion with a full selectivity to PG3

Summary

Introduction

Polyglycerols (PGs) are very interesting polyols with a wide range of structures and applications, in the cosmetics, biomedical, and food sectors. Considering the wide availability of Ca, its low cost, and its absence of toxicity in the case of catalyst leaching into the media, Ca-based catalysts can be especially considered promising for glycerol polymerization reactions [9,12]. Such catalysts usually exhibit a moderate selectivity to PG2-3. Kirby et al [3] reported a 45% selectivity to PG2-3 at full glycerol conversion in the presence of CaO/CNF. Barros et al [4] reported 55% selectivity to PG2-3 at glycerol conversion of 90% in the presence of dolomite (CaCO3·MgCO3)

Methods

Results

Discussion

Conclusion